The reading of electrical energy, water flow, and gas usage has historically been accomplished with human meter readers who came on-site and manually documented meter readings. Over time, this manual meter reading methodology has been enhanced with walk by or drive by reading systems that use radio communications to and from a mobile collector device in a vehicle. Recently, there has been a concerted effort to accomplish meter reading using fixed communication networks that allow data to flow from the meter to a host computer system without human intervention.
Utility meters that use radio communications to send data to and receive data from a mobile collector device include antennas for emitting radio signals and for receiving radio signals from the mobile collector device. In a typical utility meter, an antenna isolation board provides high voltage isolation between external antenna components and meter line voltages. Insufficient high voltage isolation may compromise the safety of the utility meter by potentially exposing a user who touches the antenna to the line voltage that powers the utility meter. In addition, insufficient high voltage isolation may adversely affect the performance of the utility meter by leaving the internal components of the utility meter vulnerable to electrical discharges to the antenna, e.g., during electrical storms.
In order to satisfy commonly accepted industry specifications, the antenna isolation board should provide at least 5 kV of voltage isolation between the antenna or an antenna cable attached to the antenna and any internal components of the utility meter, including, for example, a radio frequency (RF) port. Additionally, the antenna isolation board should provide a low loss RF path between the antenna cable and the RF port over the entire operating frequency range. Further, it is desirable for the antenna isolation board to offer electrostatic discharge (ESD) protection for the internal components of the utility meter by presenting a low impedance across the antenna cable terminals for voltage transients induced on the antenna or antenna cable.
In some conventional utility meters, the antenna isolation board is implemented using high voltage capacitors and a shunt element, such as an inductor or a resonant stub. The capacitors provide voltage isolation between antenna coaxial and radio RF connections. The shunt element provides ESD and transient protection for the RF input. This type of circuit can provide satisfactory RF performance, but the high voltage capacitors required for implementing the circuit are relatively expensive. Further, it is usually necessary to apply a dielectric overcoating to the capacitors and the areas surrounding the capacitors to meet voltage isolation requirements due to the small terminal spacings for available capacitors. Applying the dielectric overcoating generally involves a manual secondary process. Normal application variances can cause substantial variability in the antenna board voltage isolation and RF performance.
Accordingly, a need exists for an antenna isolation board that provides high voltage isolation between an antenna or antenna cable and the internal components of a utility meter while avoiding the shortcomings of conventional implementations.